Interactions in accordance with coulomb's law between conduction electrons in massive metals provides the basis for a collective excitation branch to exist that is related to the oscillation of the charge density (volume plasmons). In bounded metal samples beside volume plasmons with the frequency: ##EQU1## wherein .eta. is electron density, .epsilon. and m are the charge and rest mass, respectively, of the electron, there exist surface plasmons related to oscillations of the surface charge density. For example, in metal spheres a set of surface plasmon oscillations may be excited characterized by the multipolarity L of their eigenfunctions. The frequencies of these plasmons are defined by the equation: ##EQU2## wherein .omega..sub.o is as identified hereinabove and L is multipolarity. The result of the above equation is valid for sufficiently large particles.
The above background information is well documented in the literature. A compilation of a wide cross-section of activity on electromagnetic surface modes is found in "Electromagnetic Surface Modes", edited by A. D. Boardman, copyright 1982 by John Wiley & Sons Ltd. The physical properties of bulk matter when fragmentation of the bulk matter has taken place is very striking in the effect to the charges in electromagnetic characteristics of metals of their behavior in external electromagnetic fields. Their behavior in external electromagnetic fields is determined mainly by the collective motion of conduction electrons which is affected strongly by their scattering on particle boundaries. The teaching, as noted in Chapter 8, of citation edited by Boardman, titled: "Electromagnetic surface modes in small metallic particles" by A. A. Lushnikov et al, indicates that the role of scattering on particle boundaries increases as the size of the particle decreases.
The extensive investigations of small (1-10 nanometers, nm) metal particles have been of great interest in research in the field of physics as evidenced in the increasing application of dispersed materials. However, many experimental investigations of small metal particles when subjected to an external electromagnetic field have revealed the existence of some anomalies. In attempts to meet the need to understanding these anomalies a number of theoretical approaches have ensued which conclude that a small metal particle is considered as a bounded gas of free conduction electrons. The model developed is the so-called jellium model which in combination with random phase approximation (RPA) yields a systematic account of the quantum mechanical theory of the electromagnetic properties of small metal particles. Chapter 8, Section 4 by Lushnikov et al (cited hereinabove) is devoted to a study of the size dependence of the surface plasmon peak position in small metal particles.
As a result of recent studies by applicant and others (Kennerly et al, Phys. Rev. B 29, 2926 (1984); Bloemer et al, Phys. Rev. B 37, 8015 (1988); and Bloemer et al, J. Opt. Soc. Am. B5, 2552 (1988)), the optical properties of heated silver films, optical properties of submicrometer-size silver needles, and surface electromagnetic modes in prolate spheroids of gold, aluminum, and copper have shown that small oblate and prolate spheroidal particles support two surface plasmon modes. One of the surface plasmon modes is a dipole oriented along the major axis of the spheroid while the other is a dipole oriented along the minor axis of the spheroid.
The above background information and noted research in the field of physics have provided applicant the motivation to apply the results of research to utilize the surface plasmon resonance in submicrometer-size particles to polarize electromagnetic radiation.
Therefore, an object of the invention is to provide a waveguide polarizer which utilizes localized surface plasmon resonances in submicrometer-size particles to polarize electromagnetic radiation.
Another object of this invention is to provide submicrometer metallic particles which are nonspherical in order to have the anisotropy required for polarizers.
A further object of this invention is to provide metallic particles which are positioned in a waveguide so that the metallic particles can be reached by the electromagnetic field propagating in the waveguide whereby a portion of the electromagnetic radiation is absorbed and a portion is passed to achieve polarization.